Eye-tracking and its application in medicine

Literally, the term eye tracking (sometimes known by the name gaze tracking) means following an eye. It is a process during which specific devices determine the position of the patient's eyeballs. Depending on where the eye is directed, the system calculates the angle of view, and thus makes it possible to determine which of several objects a person looks at. Devices used for this purpose are called eye trackers.

Eye tracking is used in various areas, mostly in the medical and ophthalmic research, commercial applications to determine the usability of websites and printed materials, in the creation of various simulators and systems of augmented reality, in modern video surveillance, and so on. Eye trackers are also actively used in specialized medical centers to create a system of communication with patients who have partially or totally lost their motor function, those suffering from serious lesions of the musculoskeletal system, or speech disorders. For such patients, not only physiological, but also psychological and social rehabilitation is important. For this reason the communication for them has an important role.

There are different types of eye trackers, and the main difference between them is the type of the technology used to determine the position of the eyes.

The first type of device is a set of special electrodes, positioned around the patient's eyes. Since each eye is a constant source of a weak electric field, with the help of special equipment the position of the pupil at a fixed point in time can be determined. This method does not require high computing power, can be used in total darkness, with the patient’s eyes closed, but is more suitable for medical research, rather than to facilitate the communication between the patient and his assistant.

The second type eye trackers use is miniature mirrored lenses. To function accurately these devices require full physical contact with the patient's eyes. They accurately identify fast dynamics of eye rotation and are used by ophthalmologists to determine the physiology of the eye movements of each individual patient. Like the first type of eye trackers, mirrored lenses are also designed exclusively for medical and surgical purposes.

The third type of eye-tracking devices is a system of automatic backlight and video recording in real-time which, using computer processing, calculates the position of the pupil, and according to the coordinates, determines with sufficient accuracy the direction of the patient’s gaze. These systems are used in the patient’s communication with the medical staff, doctors, and visitors. Their principle of operation is similar to working with an assistant, but the last one is replaced by the computer system. On the screen the patient sees a matrix of letters already usual to him; by his gaze he can point to the desired character, then with a single or double blink or other pre-defined eye movement, select it. In this manner the patient selects the letters and composes the words and the sentences.

The advantages of such a computer system are obvious. First of all, a constant presence of the assistant near the paralyzed patient is not required. The patient can choose himself the rest periods that suit him. The system will be put on hold while the patient is sleeping or not composing the text. In case of an error there is no need for patient or assistant to type a word or a phrase from the beginning because computer eye trackers allow editing the text. And finally, the most obvious advantage is that a paralyzed person can prepare a message in advance, for example, write a greeting for visitors or a few words about his health during regular medical inspection. By the way, most eye trackers in medical health care facilities are equipped with a function designed to call in a doctor. To do so the patient only needs to focus his gaze for a while on the area of ​​the screen responsible for this.

At first glance, it appears that the electronic eye-tracking systems are devoid of all shortcomings of personal contact of the patient with the assistant, but it is not. First, keeping the patient in a specialized clinic is much more expensive, and secondly, many professional eye trackers used in medical centers are too cumbersome and inconvenient; working with them make patients tire easily. Finally, it does not solve the problems of those paralyzed people whose therapy and rehabilitation should be carried out step by step at home.